Multivariable Control With Changed Interaction For Disturbance Rejection

Most industrial processes can be regarded as a more input more output(MIMO)system.In MIMO systems,there is often a complex coupling relationship between loops,which makes the design of feedback controllers difficult.The traditional method to deal with the coupling between loops of multivariable control systems is to design a decoupler to remove the coupling between loops.However,the research shows that the coupling between loops may strengthen or weaken the influence of disturbance on output.Therefore,from the point of view of disturbance rejection,decoupling control or decentralized control may not be the best choice.Inspired by this discovery,many scholars have proposed a generalized decoupling control strategy.The main idea of generalized decoupling control is to evaluate the effect of coupling on disturbance by using relative disturbance gain or relative load gain.Then a generalized decoupler is designed to remove the coupling which is not conducive to the effect of disturbance suppression and retain the coupling which is conducive to disturbance suppression.However,the relative disturbance gain can only evaluate the effect of coupling on the open-loop gain from disturbance to output.The disturbance rejection ability of the control system is related to many factors,such as forward channel transfer function,disturbance channel transfer function,controller parameters and so on.Therefore,simply using relative disturbance gain or relative load gain to evaluate the effect of coupling on disturbance suppression of control system sometimes leads to wrong results.Because of the above limitations,the generalized decoupling control sometimes can not achieve the desired disturbance rejection effect.In this paper,we improve the traditional generalized decoupling control.Firstly,we improved the index used to evaluate the effect of coupling on disturbance,so that it can dynamically show the effect of coupling on the open-loop gain from disturbance to output at different frequencies.Then we change the design of the generalized decoupling decoupler so that those loops that do not need decoupling are consistent with the ideal decoupling control in the forward channel transfer function.If the open-loop gain from disturbance to output can always be suppressed by the internal coupling of the working frequency of the loop,a better interference suppression effect will be achieved in the loop.The main idea of generalized decoupling control is to make full use of the coupling relationship of the loop itself to improve the disturbance rejection ability of the system.But sometimes the coupling of the loop itself is not conducive to improving the disturbance rejection ability of the system.It must be removed,and some help to improve the disturbance rejection ability of the system is limited.Based on the hypothesis of perfect control,the relationship between coupling and disturbance to output transfer function is obtained through a comparative study of decoupling control and decentralized control.Then we design a variable coupling matrix to adjust the coupling between loops so as to maximize the impact of disturbance on the output of control system.Finally,we will illustrate the proposed method and prove its effectiveness through simulations.